1. Field of the Invention
The present invention relates to an apparatus for recording an image on a sheet such as a recording paper.
2. Related Background Art
In continuous operation of a conventional image forming apparatus employing image forming sheets or ink sheets, a succeeding sheet is usually is fed into an image forming path after a preceding sheet is subjected to an image forming operation but before said preceding sheet is discharged from the apparatus or before said sheet reaches a stacking position in the apparatus, in order to reduce the time required for image forming process in such continuous operation. Consequently, in such continuous operation of the image forming apparatus, plural sheets are present in the transport path in the apparatus.
For example, in an electrophotographic color image forming apparatus in which toner images obtained by developing, with colored toners, electrostatic latent images formed on a photosensitive member are transferred, in registration, on a sheet material borne on a transfer drum, a succeeding sheet material may be already fed into the apparatus and placed on said transfer drum while a preceding sheet material is still in a fixing station which is the final stage of the image forming process.
Also in image forming apparatus in which an image is formed by thermal transfer or ink jet on an imaging sheet supported on a rotary cylindrical member, a succeeding sheet material may be fed into the apparatus and placed on said cylindrical member while a preceding sheet is still in a transport unit toward the exit of the apparatus after being detached from said cylindrical member.
Also in image forming apparatus in which a sheet material other than the final image bearing sheet, such as a thermal ink sheet or a photosensitive master sheet, is supported on a rotary member, a succeeding sheet material may be already fed into the apparatus and placed on said rotary member while a preceding sheet is still in a transport path toward a determined stacking position after being separated from said rotary member.
On the other hand, when a succeeding sheet is placed on the rotary member, a preceding sheet which has completed image formation may still be on a discharge path.
Consequently, such image forming apparatus is usually so constructed, in case of an abnormality such as sheet jamming in the transport path, as to display such abnormality and to immediately stop all the driven parts such as transport means and image recording means, thus urging the operator to effect an appropriate countermeasure.
However, in such image forming apparatus, in case of a trouble in the transportation of a sheet material in the transport path, the operator has to remove not only the sheet that has caused said trouble but also a sheet on the rotary member since such sheet is no longer usable. This fact results in following drawbacks:
(1) Cumbersome sheet removal:
The sheet removal is very cumbersome as plural sheets have to be removed, with confirmation of positions of said sheets:
(2) Waste of sheet to be removed from the rotary member:
The sheet in the course of image forming process on the rotary member has to be removed and wasted even in case of a trouble in a sheet in the transport path:
(3) Waste of ink, toner etc. caused by the removal of sheet in the image forming process on the rotary member:
Removal of the sheet in the course of image forming process on the rotary member leads to waste of ink or toner employed in image formation: and
(4) Poor image obtained on the sheet on the rotary member if the image forming process is interrupted:
For example, if the transfer drum of an electrophotographic image forming apparatus is stopped in the course of an image forming process, uniform image formation cannot be expected due to uneven image transfer in an area corresponding to the change in rotating speed. Also in an image forming apparatus for forming an image by digital dots on a sheet material, a change in rotating speed as explained above results in a change in the dot pitch, thus causing unevenness in the obtained image.